Re: [PATCH 06/31] vhost: Route guest->host notification through shadow virtqueue

[Jason Wang]

在 2022/1/22 上午4:27, Eugenio Pérez 写道:
> At this moment no buffer forwarding will be performed in SVQ mode: Qemu
> just forward the guest's kicks to the device. This commit also set up
> SVQs in the vhost device.
>
> Host memory notifiers regions are left out for simplicity, and they will
> not be addressed in this series.


I wonder if it's better to squash this into patch 5 since it gives us a 
full guest->host forwarding.


> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>   include/hw/virtio/vhost-vdpa.h |   4 ++
>   hw/virtio/vhost-vdpa.c         | 122 ++++++++++++++++++++++++++++++++-
>   2 files changed, 124 insertions(+), 2 deletions(-)
>
> diff --git a/include/hw/virtio/vhost-vdpa.h b/include/hw/virtio/vhost-vdpa.h
> index 3ce79a646d..009a9f3b6b 100644
> --- a/include/hw/virtio/vhost-vdpa.h
> +++ b/include/hw/virtio/vhost-vdpa.h
> @@ -12,6 +12,8 @@
>   #ifndef HW_VIRTIO_VHOST_VDPA_H
>   #define HW_VIRTIO_VHOST_VDPA_H
>   
> +#include <gmodule.h>
> +
>   #include "hw/virtio/virtio.h"
>   #include "standard-headers/linux/vhost_types.h"
>   
> @@ -27,6 +29,8 @@ typedef struct vhost_vdpa {
>       bool iotlb_batch_begin_sent;
>       MemoryListener listener;
>       struct vhost_vdpa_iova_range iova_range;
> +    bool shadow_vqs_enabled;
> +    GPtrArray *shadow_vqs;
>       struct vhost_dev *dev;
>       VhostVDPAHostNotifier notifier[VIRTIO_QUEUE_MAX];
>   } VhostVDPA;
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index 6c10a7f05f..18de14f0fb 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -17,12 +17,14 @@
>   #include "hw/virtio/vhost.h"
>   #include "hw/virtio/vhost-backend.h"
>   #include "hw/virtio/virtio-net.h"
> +#include "hw/virtio/vhost-shadow-virtqueue.h"
>   #include "hw/virtio/vhost-vdpa.h"
>   #include "exec/address-spaces.h"
>   #include "qemu/main-loop.h"
>   #include "cpu.h"
>   #include "trace.h"
>   #include "qemu-common.h"
> +#include "qapi/error.h"
>   
>   /*
>    * Return one past the end of the end of section. Be careful with uint64_t
> @@ -409,8 +411,14 @@ err:
>   
>   static void vhost_vdpa_host_notifiers_init(struct vhost_dev *dev)
>   {
> +    struct vhost_vdpa *v = dev->opaque;
>       int i;
>   
> +    if (v->shadow_vqs_enabled) {
> +        /* SVQ is not compatible with host notifiers mr */


I guess there should be a TODO or FIXME here.


> +        return;
> +    }
> +
>       for (i = dev->vq_index; i < dev->vq_index + dev->nvqs; i++) {
>           if (vhost_vdpa_host_notifier_init(dev, i)) {
>               goto err;
> @@ -424,6 +432,17 @@ err:
>       return;
>   }
>   
> +static void vhost_vdpa_svq_cleanup(struct vhost_dev *dev)
> +{
> +    struct vhost_vdpa *v = dev->opaque;
> +    size_t idx;
> +
> +    for (idx = 0; idx < v->shadow_vqs->len; ++idx) {
> +        vhost_svq_stop(g_ptr_array_index(v->shadow_vqs, idx));
> +    }
> +    g_ptr_array_free(v->shadow_vqs, true);
> +}
> +
>   static int vhost_vdpa_cleanup(struct vhost_dev *dev)
>   {
>       struct vhost_vdpa *v;
> @@ -432,6 +451,7 @@ static int vhost_vdpa_cleanup(struct vhost_dev *dev)
>       trace_vhost_vdpa_cleanup(dev, v);
>       vhost_vdpa_host_notifiers_uninit(dev, dev->nvqs);
>       memory_listener_unregister(&v->listener);
> +    vhost_vdpa_svq_cleanup(dev);
>   
>       dev->opaque = NULL;
>       ram_block_discard_disable(false);
> @@ -507,9 +527,15 @@ static int vhost_vdpa_get_device_id(struct vhost_dev *dev,
>   
>   static int vhost_vdpa_reset_device(struct vhost_dev *dev)
>   {
> +    struct vhost_vdpa *v = dev->opaque;
>       int ret;
>       uint8_t status = 0;
>   
> +    for (unsigned i = 0; i < v->shadow_vqs->len; ++i) {
> +        VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs, i);
> +        vhost_svq_stop(svq);
> +    }
> +
>       ret = vhost_vdpa_call(dev, VHOST_VDPA_SET_STATUS, &status);
>       trace_vhost_vdpa_reset_device(dev, status);
>       return ret;
> @@ -639,13 +665,28 @@ static int vhost_vdpa_get_vring_base(struct vhost_dev 
> *dev,
>       return ret;
>   }
>   
> -static int vhost_vdpa_set_vring_kick(struct vhost_dev *dev,
> -                                       struct vhost_vring_file *file)
> +static int vhost_vdpa_set_vring_dev_kick(struct vhost_dev *dev,
> +                                         struct vhost_vring_file *file)
>   {
>       trace_vhost_vdpa_set_vring_kick(dev, file->index, file->fd);
>       return vhost_vdpa_call(dev, VHOST_SET_VRING_KICK, file);
>   }
>   
> +static int vhost_vdpa_set_vring_kick(struct vhost_dev *dev,
> +                                       struct vhost_vring_file *file)
> +{
> +    struct vhost_vdpa *v = dev->opaque;
> +    int vdpa_idx = vhost_vdpa_get_vq_index(dev, file->index);
> +
> +    if (v->shadow_vqs_enabled) {
> +        VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs, vdpa_idx);
> +        vhost_svq_set_svq_kick_fd(svq, file->fd);
> +        return 0;
> +    } else {
> +        return vhost_vdpa_set_vring_dev_kick(dev, file);
> +    }
> +}
> +
>   static int vhost_vdpa_set_vring_call(struct vhost_dev *dev,
>                                          struct vhost_vring_file *file)
>   {
> @@ -653,6 +694,33 @@ static int vhost_vdpa_set_vring_call(struct vhost_dev *dev,
>       return vhost_vdpa_call(dev, VHOST_SET_VRING_CALL, file);
>   }
>   
> +/**
> + * Set shadow virtqueue descriptors to the device
> + *
> + * @dev   The vhost device model
> + * @svq   The shadow virtqueue
> + * @idx   The index of the virtqueue in the vhost device
> + */
> +static bool vhost_vdpa_svq_setup(struct vhost_dev *dev,
> +                                VhostShadowVirtqueue *svq,
> +                                unsigned idx)
> +{
> +    struct vhost_vring_file file = {
> +        .index = dev->vq_index + idx,
> +    };
> +    const EventNotifier *event_notifier;
> +    int r;
> +
> +    event_notifier = vhost_svq_get_dev_kick_notifier(svq);


A question, any reason for making VhostShadowVirtqueue private? If we 
export it in .h we don't need helper to access its member like 
vhost_svq_get_dev_kick_notifier().

Note that vhost_dev is a public structure.


> +    file.fd = event_notifier_get_fd(event_notifier);
> +    r = vhost_vdpa_set_vring_dev_kick(dev, &file);
> +    if (unlikely(r != 0)) {
> +        error_report("Can't set device kick fd (%d)", -r);
> +    }


I wonder whether or not we can generalize the logic here and 
vhost_vdpa_set_vring_kick(). There's nothing vdpa specific unless the 
vhost_ops->set_vring_kick().


> +
> +    return r == 0;
> +}
> +
>   static int vhost_vdpa_dev_start(struct vhost_dev *dev, bool started)
>   {
>       struct vhost_vdpa *v = dev->opaque;
> @@ -660,6 +728,13 @@ static int vhost_vdpa_dev_start(struct vhost_dev *dev, 
> bool started)
>   
>       if (started) {
>           vhost_vdpa_host_notifiers_init(dev);
> +        for (unsigned i = 0; i < v->shadow_vqs->len; ++i) {
> +            VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs, i);
> +            bool ok = vhost_vdpa_svq_setup(dev, svq, i);
> +            if (unlikely(!ok)) {
> +                return -1;
> +            }
> +        }
>           vhost_vdpa_set_vring_ready(dev);
>       } else {
>           vhost_vdpa_host_notifiers_uninit(dev, dev->nvqs);
> @@ -737,6 +812,41 @@ static bool  vhost_vdpa_force_iommu(struct vhost_dev *dev)
>       return true;
>   }
>   
> +/**
> + * Adaptor function to free shadow virtqueue through gpointer
> + *
> + * @svq   The Shadow Virtqueue
> + */
> +static void vhost_psvq_free(gpointer svq)
> +{
> +    vhost_svq_free(svq);
> +}


Any reason for such indirection? Can we simply use vhost_svq_free()?

Thanks


> +
> +static int vhost_vdpa_init_svq(struct vhost_dev *hdev, struct vhost_vdpa *v,
> +                               Error **errp)
> +{
> +    size_t n_svqs = v->shadow_vqs_enabled ? hdev->nvqs : 0;
> +    g_autoptr(GPtrArray) shadow_vqs = g_ptr_array_new_full(n_svqs,
> +                                                           vhost_psvq_free);
> +    if (!v->shadow_vqs_enabled) {
> +        goto out;
> +    }
> +
> +    for (unsigned n = 0; n < hdev->nvqs; ++n) {
> +        VhostShadowVirtqueue *svq = vhost_svq_new();
> +
> +        if (unlikely(!svq)) {
> +            error_setg(errp, "Cannot create svq %u", n);
> +            return -1;
> +        }
> +        g_ptr_array_add(v->shadow_vqs, svq);
> +    }
> +
> +out:
> +    v->shadow_vqs = g_steal_pointer(&shadow_vqs);
> +    return 0;
> +}
> +
>   static int vhost_vdpa_init(struct vhost_dev *dev, void *opaque, Error **errp)
>   {
>       struct vhost_vdpa *v;
> @@ -759,6 +869,10 @@ static int vhost_vdpa_init(struct vhost_dev *dev, void 
> *opaque, Error **errp)
>       dev->opaque =  opaque ;
>       v->listener = vhost_vdpa_memory_listener;
>       v->msg_type = VHOST_IOTLB_MSG_V2;
> +    ret = vhost_vdpa_init_svq(dev, v, errp);
> +    if (ret) {
> +        goto err;
> +    }
>   
>       vhost_vdpa_get_iova_range(v);
>   
> @@ -770,6 +884,10 @@ static int vhost_vdpa_init(struct vhost_dev *dev, void *opaque, Error **errp)
>                                  VIRTIO_CONFIG_S_DRIVER);
>   
>       return 0;
> +
> +err:
> +    ram_block_discard_disable(false);
> +    return ret;
>   }
>   
>   const VhostOps vdpa_ops = {